Cholangiopathies, such as primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC), are characterized by damage and dysfunction of bile duct epithelial cells (cholangiocytes). Recently, long noncoding RNAs (lncRNAs) have been identified as a novel class of master regulators of gene expression and are linked to many fundamental biological processes and various human diseases including various liver diseases. However, little is known regarding the role of lncRNAs in the regulation of cholangiocyte function and pathogenesis of hepatobiliary diseases. The overall goal of the current application is to identify the roles and mechanisms of lncRNAs in biliary dysfunction under cholestatic conditions and to create a fundamental base for developing novel therapeutic strategies for cholangiopathies. The expression of lncRNAs is tissue-, cell type- and differentiation stage-specific. LncRNA H19 is the first identified imprinted lncRNA and is highly conserved across lineages. It has been reported that H19 is the most strongly differentially expressed lncRNA during liver development and has been linked to hepatic metastases from a range of human carcinomas and cholestatic liver injury. However, the regulatory role of H19 in cholangiocyte pathophysiology remains unknown and is the focus of the current application. Our most recent studies discovered that H19 is highly expressed in cholangiocytes, but not in hepatocytes under physiological conditions and hepatic H19 expression levels are correlated with upregulation of S1PR2 and cholestatic liver injury in the multi-drug resistance 2 knockout (Mdr2-/-) mouse, a well- established mouse model of PSC and PSC patient liver. Our preliminary data further showed that 1) BDL significantly up-regulated H19 and down-regulated the apical sodium bile acid transporter (ASBT) and sodium/taurocholate co-transporting polypeptide (NTCP); 2) BDL-induced cholestatic liver injury was markedly reduced in H19?Exon1/+ mouse; 3) Knocking down H19 not only significantly reduced taurocholate (TCA)- induced expression of fibrotic genes and S1PR2 in cholangiocytes, but also markedly upregulated hepatic small heterodimer partner (SHP) expression and reduced cholestatic injury in Mdr2-/- mice; 4) Hepatic H19 level was also significant upregulated in the carbon tetrachloride (CCl4)-induced cholestatic liver injury mouse model. Based on these observations, we HYPOTHESIZE that lncRNA H19 plays an important role in the regulation of hepatobiliary epithelial function by disruption of hepatic bile acid homeostasis. Two specific aims are proposed to test this hypothesis. 1) To define the role of lncRNA H19 in the regulation of bile acid-mediated cholangiocyte growth and remodeling during cholestatic liver injury; 2) To identify the mechanisms by which bile acids upregulate lncRNA H19 in cholestatic conditions. Completion of the proposed studies will make a significant conceptual advance by linking the lncRNA H19-mediated regulation of biliary epithelial function with cholestatic biliary injury in patients with cholangiopathies and will provide a translational mechanism for how bile acids and lncRNA H19 mediate hepatobiliary fibrosis.